Greater V 02 peak is correlated with greater skeletal muscle deoxygenation amplitude and hemoglobin concentration within individual muscles during ramp-incremental cycle exercise

It is axiomatic that greater aerobic fitness (Vo2peak) derives from enhanced perfusive and diffusive O2 conductances across active muscles. However, it is unknown how these conductances might be reflected by regional differences in fractional O2 extraction (i.e., deoxy[Hb+Mb] and tissue O2 saturation [StO2]) and diffusive O2 potential (i.e., total[Hb+Mb]) among muscles spatially heterogeneous in blood flow, fiber type, and recruitment (vastus lateralis, VL; rectus femoris, RF). Using quantitative time-resolved near infrared spectroscopy during ramp cycling in 24 young participants (Vo2peak range, ~37.4-66.4 ml ･ kg-1 ･ min-1), we tested the hypotheses that (1) deoxy[Hb+Mb] and total[Hb+Mb] at Vo2peak would be positively correlated with Vo2peak in both VL and RF muscles; (2) the pattern of deoxygenation (the deoxy[Hb+Mb] slopes) during submaximal exercise would not differ among subjects differing in Vo2peak. Peak deoxy[Hb+Mb] and StO2 correlated with Vo2peak for both VL (r = 0.44 and -0.51) and RF (r = 0.49 and -0.49), whereas for total[Hb+Mb] this was true only for RF ( r= 0.45). Baseline deoxy[Hb+Mb] and StO2 correlated with Vo2peak only for RF (r = -0.50 and 0.54). In addition, the deoxy[Hb+Mb] slopes were not affected by aerobic fitness. In conclusion, while the pattern of deoxygenation (the deoxy[Hb+Mb] slopes) did not differ between fitness groups the capacity to deoxygenate [Hb+Mb] (index of maximal fractional O2 extraction) correlated significantly with Vo2peak in both RF and VL muscles. However, only in the RF did total[Hb+Mb] (index of diffusive O2 potential) relate to fitness.